1. Field of the Invention
The present invention relates to a method of fabricating a liquid lens containing at least two liquids and a liquid lens fabricated thereby, and more particularly, to a method of fabricating a liquid lens which applies voltage to a chamber containing liquids to induce electrowetting, thereby preventing unstable movement of the liquids when sealing a hole containing the liquids, and a liquid lens fabricated thereby.
2. Description of the Related Art
A general lens module uses lenses manufactured with solid material such as glass at a fixed focal distance. In such a lens module, a plurality of solid lenses are provided and the distance of each lens is adjusted to control the focus. Thus, such a lens module is limited in miniaturization and requires a complicated operation to adjust focus.
To overcome such problems, there has been proposed a liquid lens which is configured to adjust the focus by varying the curvature of meniscus between the different liquids. This liquid lens has a simple internal configuration to facilitate miniaturization and to more easily adjust the focus.
Since the researches on the liquid lens utilizing electrowetting have gained attention in early 2000, various applications have been introduced, and efforts for its industrialization have been accelerated. In general, liquid lenses have advantages such as small size, low power consumption, prompt response rate and good reproducibility. Therefore, auto-focusing modules for cameras mounted to mobile phones, PDAs and the like have continued to be actively developed.
A conventional method of fabricating a liquid lens will now be explained hereunder with reference to the accompanying drawings.
FIG. 1 is a sectional view illustrating a conventional method of fabricating a liquid lens, in which liquid is filled in a hole inside a chamber, FIG. 2 is a sectional view illustrating the conventional method of fabricating a liquid lens, in which an upper transparent plate is in contact with electrolyte, and FIG. 3 is a sectional view illustrating the conventional method of fabricating a liquid lens in which the upper transparent plate is attached to an upper surface of the chamber to seal the hole.
The conventional method of fabricating the liquid lens is as follows in detail.
First, as shown in FIG. 1, a chamber 100 having an inner wall to form a hole 110 with a circular section is provided. The lower surface of the hole 110 is sealed by a lower transparent plate 120, and thus the lower transparent plate 120 and the chamber 100 are bonded to each other by a bonding layer (not shown). In addition, a hydrophobic insulation film is coated on an inner wall of the hole 110 to allow the operation of the liquid lens.
When the chamber 100 is provided, two non-miscible liquids 300 and 400 are filled in the hole 110. At this time, these two liquids are provided in substantially the same proportions but have different refractive indices. One is conductive while the other one is non-conductive. In general, the liquid on the top is electrolyte 300 having conductivity whereas the liquid at the bottom is insulation liquid 400 having non-conductivity.
When the liquids are filled in the hole 110, the electrolyte 300 at the top tends to dewet to an inner wall of the hole 110 whereas the insulation liquid 400 tends to wet an inner wall of the hole 110. At this time, due to affinity difference between the two liquids and an insulation film formed on an inner wall of the hole 110, the insulation liquid 400 wetting the inner wall of the hole 110 tends to enclose the electrolyte 300 as shown in FIG. 1. That is, the meniscus between the electrolyte 300 and the insulation liquid 400 has a concave central portion.
In addition, the upper surface of the electrolyte 300 filled in the hole 110 has an upwardly-convexed shape due to surface tension. And when the upper transparent plate 500 attached to an upper surface of the chamber 100 comes in contact with the electrolyte 300, the electrolyte 300 adheres to an undersurface of the upper transparent plate 500 due to mutual attraction, as shown in FIG. 2.
When the electrolyte 300 adheres to an undersurface of the upper transparent plate 500 as described above, the insulation liquid 400 is also pulled toward the upper transparent plate 500 and its peripheral portion is positioned near an upper opening of the hole 110. In this state, when the upper transparent plate 500 is attached to an upper end of the chamber 100, the electrolyte 300 leaks between an upper surface of the chamber 100 and an undersurface of the upper transparent plate 500, and the insulation liquid 400 also is pulled along with the electrolyte 300 to leak between an upper surface of the chamber 100 and an undersurface of the upper transparent plate 500. The leakage of the electrolyte 300 and the insulation liquid 400 as described above may cause optical and operational problems of the lens, degrade the sealing state of the liquids and cause bubbles to be formed inside the hole 110. The bubble formation in the hole 110 hinders maintenance of a regulated level of refractive index of light, thus fatally impairing the normal function of the lens.
Besides the problematic bubble formation in the hole 110, when the upper transparent plate 500 is attached, if the insulation liquid 400 wraps around the entire inner surface of the hole 110 as shown in FIG. 3, current is not applied to the electrolyte 300 even with voltage application, impeding electrowetting. Without the electrowetting, the meniscus between the electrolyte 300 and the insulation liquid 400 is not changed, making it impossible to adjust focus.
In addition, when desired to inject additional liquid before finally attaching the upper transparent plate 500, additional injection of liquid into the hole in a state depicted in FIG. 2 results in leakage of a peripheral portion of the insulation liquid to the outside, due to the pressure of the liquid being additionally injected.
To overcome such a problem, the hole 110 should be formed deeper, which entails increased thickness of the chamber 100, resulting in an increased overall size of the liquid lens.